Flywheels are generally known in the art for storing energy. While flywheel energy storage devices have been used for many years in satellite or other spacecraft applications, more recently they have been adapted for use on terrestrial machines. More specifically, hybrid power plants have been proposed which use a combustion engine as the primary mover and a flywheel as a secondary mover.
In some applications, the flywheel is operably coupled directly to an engine output, such as a crankshaft, upstream of a transmission. The flywheel may add to or subtract from power supplied by the engine to the transmission and, ultimately, one or more driven wheels. In this arrangement, the flywheel may also be configured to use regenerative braking, in which the flywheel is sped up to capture kinetic energy of the machine as it decelerates. Conversely, when the machine is accelerating, the flywheel may provide additional power to the wheels, thereby reducing flywheel speed. The position of the flywheel upstream of the transmission may allow it to efficiently spin up to a desired operating speed during start up. During regenerative braking, however, the energy from the ground engaging members may be transmitted through several mechanical connections, including the transmission, before it reaches the flywheel. Consequently, the amount of energy that can be captured by an upstream-located flywheel may be reduced by the mechanical losses as it travels through the transmission and other mechanical connections, thereby decreasing the efficiency of the flywheel.
In other applications, the flywheel may be operably coupled to a drivetrain output downstream of the transmission. When the machine decelerates, energy from the drivetrain (and an associated transmission) may be transferred to the flywheel. During acceleration of the machine, energy from the flywheel may be transferred to the powertrain to assist with the increased power demand. When positioned downstream of the transmission, the flywheel may more efficiently capture energy during regenerative braking due to the decrease in mechanical connections between the flywheel and the ground engaging members, thereby reducing the mechanical loss. During start up, however, the drivetrain may not be configured to spin up the flywheel during machine start up. Additionally, the location of the flywheel downstream of the transmission may make such spin up inefficient due to mechanical loss through the transmission.
U.S. Pat. No. 4,499,965 to Oetting et al. discloses a hybrid drive that includes both an engine flywheel and a storage flywheel. The engine flywheel is configured to compensate for non-uniformities in engine output torque, while the storage flywheel is configured to store energy during regenerative braking Both the engine flywheel and the storage flywheel are positioned upstream of the transmission, and therefore suffer from the drawbacks noted above. Conversely, U.S. Patent Application Publication No. 2010/0152984 to Bowman et al. discloses a hybrid vehicle having a flywheel connected to a lower powertrain assembly, downstream of a transmission. The flywheel of Bowman et al. is not coupled to the engine, and therefore is incapable of engine-powered spin up.